Electrical devices containing alkyl beta-alkoxypropionates



Jan. 20, 1959 s. A. HEININGER 1 2,870,236

ELECTRICAL DEVICES CONTAINING ALKYL fl-ALKOXYPROPIONATES Filed March 21, 1957 DIELECTRIC METAL CONTAIN|NG ELECTRODES AN ALKYL Fl GI ALKOXYPROPIONATE FIG-4 METAL FOIL PAPER IMPREGNATED WITH AN ALKYL ALKOXYPROPIONATE FIG-3 INVENTOR.

SAMUEL ALLEN HEININGER BY Lu, 4-.

ATTOR EY United States Patent ELECTRICAL DEVICES CONTAINING ALKYL B-ALKOXYPROPIONATES Samuel Allen I-Ieiningei, Dayton, Ohio, assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware Application March 21, 1957, Serial No. 647,710

6 Claims. (Cl. 174-17) The present invention relates to electrical devices and more particularly deals with apparatus comprising a combination of electricity conducting elements and dielectric insulating media.

The use of a dielectric is required in certain electrical equipment for the purpose of removing heat and of allowing the making of electrical contact in the absence of air or of explosive mixtures. The requirements for such dielectrics are, among other things, very high resistance to the flow of electric currents, high stability to atmospheric conditions at ordinary and at somewhat elevated temperatures, high resistance to thermal decomposition, low vapor pressure, loW congealing temperature, low inflammability and high fiash point. Preferably the dielectric should be a mobile liquid even at relatively low temperatures and should-be a good heat transfer agent.

In commercial practice, high boiling fractions of Patented Jan. 20, 1959 common to the prior art dielectric materials such as the deterioration of paper insulation and metal parts is eliminated or materially reduced. Still another object is to provide electrical apparatus having a long, useful life and good dielectric stability.

According-to the invention, these and other objects which will be hereinafter disclosed are provided by the following invention wherein there is provided electrical apparatus comprising, in combination, conducting elements disposed in spaced relationship to each other and adapted during operation of the apparatus, to have a difference in electrical potential therebetween and, interpetroleum distillates have been largely used for this purpose. These liquids do not satisfy all of the above-stated requirements. They are relatively poor heat transfer agents and under the conditions of their use they gradually decompose with the formation of undesirable products which adversely influence the electrical properties. Some of these products are tarry, and others are appreciably volatile and may present fire and explosion hazards.

Another disadvantage of the mineral oils is that they tend to form deposits generally known as sludge during the period of their use. This is due to oxidation and decomposition and also results to some extent in the formation of acids which is equally undesirable. The sludging of dielectrics during use is a serious disadvantage and requireseither replacement of the oil or treatment to remove the sludge and revivify the dielectric. A satisfactory dielectric liquid should not sludge or undergo substantial deleterious change during use and it is :one of the objects of this invention to provide a liquid which does not possess this undesirable disadvantage characteristic of the mineral oils.

The undesirable efiect of decomposition is further manifested when the mineral oils are used as capacitor impregnants. Thus, under high operating temperatures and direct current voltages, capacitors impregnated therewith undergo a characteristic type of deterioration which results in an ever increasing leakage current, a short capacitor life, visible localized decomposition of the dielectric and corrosion of the electrodes. Moreover, in

the case of capacitors operating on alternating current,

the decomposition sometimes results in an excessive in crease in power factor of the dielectric material.'

It is, therefore, an object of the present invention to provide a method for the insulation of elements in electrical apparatus wherein the above objectionable propregulators andlthe like wherein the deleterious action posed between said elements for insulating one from the other, a liquid dielectric medium comprising an alkyl 8- alkoxypropionate of the formula wherein R and R are branched chain alkyl radicals of from 8 to 18 carbon atoms.

Alkyl fi-alkoxypropionates having the above formula and useful for the present purpose are, e. g., isooctyl flisooctyloxypropionate, 2-ethylhexyl p-(2-ethylhexyloxy)- propionate, nonyl fl-nonlyoxypropionate, in which the nonyl radical is branched and is derived from the nonanol obtained according to the 0x0 process by the high pressure reaction of diisobutylene With carbon monoxide and hydrogen, decyl B-decyloxypropionate Wherein the decyl radical is branched and is derived from an 0x0 process deeanol (from propylene trimer, CO and H tert-dodecyl 8-tert-dodecyloxypropionate, 3,5,5 trimethylhexyl fl-(3,5,5 trimethylhexyloxy)propionate, S-ethyl-Z-nonyl B-(S-ethyl-Z-nonyloxy) propionate, 2- propylheptyl [3-(2-propylheptyloxy)propionate, 2,2,4- trimethyl-3-pentyl 3-(2,2,4 trimethyl 3 pentyloxy)- propionate, 3,7-dim-ethyloctyl ,6-(3,7-dimethyloctyloxy)- propionate, 3-ethyl-7-methyloctyl ,8-(3-ethyl-7-methyloctyloxy)propionate, Z-butyloctyl 8-(2-butyloctyloxy)'- propionate, 2,6,8-trimethyl-4-nonyl fi-(2,6,8-trimethyl-4- nonyloxy)propionate, Z-methyldodecyl 3-(2-methyldodecyloxy)propionate, 7-ethyl-2-rnethyl-4-undecyl B-(7-ethyl- 2-methyl-4-undecyloxy)propionate, tridecyl fi-tridecyloxypropionate, wherein the tridecyl radical is branched and is derived from an Oxo process tridecanol (from butylene trimer or propylene tetramer, CO and H 3,9-diethyl-6-tridecyl 543,9 diethyl 6 tridecyloxy)- propionate, l4-methylhexadecyl fi-(14 methylhexadecyloxy)propionate, 7-butyl-7-tetradecyl fi-(7-butyl-7-tetra decyloxy)propicnate, and 2-m-ethyl-4-tridecyl fi-(Z-methyl-4-tridecyloxy)propionate.

Mixed ether-esters, i. e., compounds in which the ether alkyl radical and the ester alkyl radical are dissimilar, are .usful, and for some purposes, even preferable to alkyl fl-alkyloxypropionates, in which both the alkyl radicals are the same. As examples of such presently useful ether csters may be mentioned decyl fl-(2-nonyloxy)propionate, in which both the decyl and the nonyl radicals are branched, the decyl radical being derived from an OX0 process decanol (from propylene trimer, CO and H and the nonyl radical from an Oxo process nonanol (from diisobutylene, CO and H 2-ethylhexyl p-tridecylo-xly propionate where the tridecyl radical is branched and is derived from OX0 process tridecanol (from propylene tetramer or butylene trimer, CO and H Z-ethylhexyl fi-decyloxypropionate where the decyl radical is branched and is derived from said 0x0 process decanol, 3,5,5-trimethylhexyl e-teredodecyloxypropionate, 2-propylheptyl fl tridecyloxypropionate wherethe tridecyl radical is branched and is derived from said Oxd process. tridecanol, branched chain nonyl B-( 3,7-dirnethyloctylo'xy)1- propionate, in which the nonyl radical is derived from said -Oxo process nonano-l, Z-butyloctyl ;8*(3-ethyl-7-methyl octyloxwpropionate, 2: hylhery fi t 9 9Y Y 9;-

pionate, 7-ethyl-2-methyl-4-undecyl fl-nonyloxypropionate where the nonyl radical is branched and is derived from said x0 process nonanol, Z-rnethyldodecyl fl-( l4- methylhexadecyloxy)propionate, decyl fi-(Z-methyli-tridecyloxy)propionate wherein the decyl radical is branched and is derived from said Oxo Process decanol-, nonyl B-decyloxypropionate wherein both the nonyl and decyl radicals are branched and are derived from said Oxof process nonanol and 0x0 process decanol, respectively, decyl fi-tridecyloxypropionate or tridecyl ,B-decyloxypropionate wherein both the decyl and tridecyl radicals are branched and are derived from said OX0 process decanol and 0x0 process tridecanol, respectively, nonyl S-tridecyloxypropionate or tridecyl fi-nonyloxypropionate wherein the nonyl and tridecyl radicals are branched and are derived from said 0x0 process nonanol and said Oxo process tridecanol, respectively.

The presently useful alkyl B-alkyloxypropionates are readily available compounds which are prepared by reaction of an appropriate alkyl acrylate with an appropriate alcohol substantially according to the scheme:

ROE-PC111 CHCOOR ROCH CH COOR' hol to the acrylate has been completed. The presently useful alkyl fi-alkyloxypropionates may also be prepared by hydrolysis of an appropriate p-alkoxypropionitrile, e. g., with aqueous sulfuric acid or by treatment of said nitrile with an appropriate alcohol and hydrochloric acid to yield the imino hydrochloride ROCH CH C :NHHCI) OR and hydrolysis of the latter.

I have found that the higher alkyl fl-alkoxypropionates serve as very useful dielectric media when interposed in electrical apparatus between metallic conducting elements that have a difference in potential during operation of the apparatus because they are very stable liquids of low freezing points and high boiling points which possess good dielectric strength, low power tivity. Examples of electrical apparatus in which the higher alkyl p-alltoxypropionates are valuable components are shown in the accompanying drawing.

Fig. 1 is a front elevation partly in section of a transformer; Fig. 2 illustrates a switch in a similar manner; Fig. 3 represents a rolled capacitor; Fig. 4 shows a sectional view of a portion of the electrodes and dielectric sheets of Fig. 3; and Fig. 5 is a side view of a cable, the casing being partly removed to permit the interior of the parts to be seen.

The transformer illustrated in Fig. 1 comprises a casing 1, core 2, coils 3 insulated with manila paper, kraft paper, cotton or other fibrous insulation, insulating and cooling medium 4, lead-in bushings 5, and suitable leads 6 connected to the coil assembly. The insulating and cooling medium may consist of a higher alkyl fl-alkoxypropionate such as branched chain nonyl fi-(2-ethylhexyloxy)propionate which may be employed as such or in combination with a highly chlorinated biphenyl such as Aroclor (manufactured by Monsanto Chemical Company, St. Louis, Mo). These two components may be employed in proportions such as from 50% to 90% by weight of the alkyl p-alkoxypropionate, with the balance being the Aroclor. Liquid hydrocarbons orother halogenated hydrocarbons or mixtures thereof may also be used in comfactor and good ohm resis- I 4 bination with the higher alkyl fl-alkoxypropionates as dielectric media, e. g., petroleum oil, halogenated compounds of naphthalene, toluene, benzene, nitrobiphenyl or diphenyl oxide.

The switch shown in Fig. 2 comprises a casing 7, fixed contacts 8 and 9, and movable contacts 10 and 11 which co-operate therewith. The movable contacts are mounted upon a support 12 which in turn is operatively connected to actuating levers 13. A suitable arc quenching liquid which may be used in this device, either as the sole dielectric, or in combination with a minor proportion of a petroleum oil or a halogenated hydrocarbon such as highly chlorinated biphenyl is nonyl B-nonyloxypropionate wherein the nonyl radical is branched and is derived from 0x0 process nonanol.

The capacitor shown in Fig. 3 is made up of alternate layers of metal foil such as aluminum or tin foil separated by sheets of dielectric material. Fig. 4 shows a section of one turn of the finished rolled capacitor illustrating the alternate electrodes and dielectric layers. Details of the construction of the paper capacitor are set forth here by way of illustration Three sheets of tissue paper (preferably ltraft capacitor tissue), are stacked upon each other, and a thin aluminum foil (about 0.0003" in thickness) is laid on the top sheet of tissue. The foil is then covered with three more sheets of the tissue and another sheet of the foil is placed there on so that the two sheets of metal foil are separated from each other by the paper. The stack of alternating layers of metal foils and tissues thus obtained is wound into a cylindrical roll. This is placed in a container, and at this point electrical connecting means, c. g., wire or bar conductors, depending upon the size of the assembly, may be connected to the metal foil in known manner. After drying, preferably in a heated vacuum oven, an allryl palkoxypropionate such as tridecyl B-tridicyloxypropionate, wherein the tridecyl radical is branched and is derived from Oxo process tridecanol is added to the container in a quantity sufficient to impregnate thoroughly the paper content thereof. The container is then sealed.

Alternatively, and particularly in the manufacture of the small items, which for the sake of economy are housed in paper tubes rather than in leak-proof containers, the tissue paper is impregnated with said alkyl B-alkoxypropionates previous to interleaving with the metal foil in the manner described above.

The cable-of Fig. 5 comprises a core 14, cable conductors 15, insulation consisting of paper or other suitable material 16 and a casing 17. The space between the insulated conductors and the casing is filled with a branched chain higher alkyl B-alkoxypropionate such as decyl l9-decyloxypropionate wherein the decyl radical is derived from 0x0 process decanol or a mixture of said propionate with substantially an equal part by weight of partially chlorinated biphenyl having from 50 to 55% by weight of combined chlorine.

A specific embodiment of the invention is the provision of dielectric liquids comprising a mixture consisting predominantly of one or more of the present branched chain, higher alkyl fl-alkoxypropionates and a minor proportion of partially chlorinated biphenyl having from, say, 40% to by weight of combined chlorine. Presently useful dielectrics will generally consist of at least 50% by weight of said propionate, with the balance being the partially chlorinated biphenyl. When designed for use in transformers, the dielectric preferably consists 80% by weight of the propionate, with the balance being a partially chlorinated biphenyl having from 60-65% by weight of combined chlorine.

A particularly valuable property of electrical apparatus comprising the present higher alkyl ,e-alkoxypropionates is their usefulness over a wide range of operating conditions. Thus, as shown below, the dielectric constant and power factor values of Z-ethylhexyl branched chain ,S-tridec'yloxypropionate (tridecyl from 0:10?

process tridecanol) at the test temperatures and frequencies indicated below:

100 O. P. S. l kc. kc. 100 kc. J.emp., C.

PF, PF, PF, PF. DK per- DK per- DK per- DK percent cent cent cent Apparatus wherein the present alkyl fi-alkoxypropionates are employed as the dielectric media are further characterized by long operating life as a consequence of the high volume resistivity of the propionates, examples of which are as follows:

1 N onyl, decyl and tridecyl radicals are all branched and derived from 0xo" process nonanol, decanol or tridecanol.

= Measured at 18 C.

Dielectric constant values and power factor values for the above branched chain alkyl fl-alkoxypropionates were determined to be as follows at a temperature of 25 C.

1 kc. 10 kc. 100 kc.

-oxypropionate PF, PF, PF,

DK per- DK per- DK percent cent cent isooctyl fl-lsooctyl 4.0 0.01 3. 9 0. 58 4. 0 0. 3S nonyl fl-nonyl. n--. 3. 8 0.73 3. 8 O. 67 3.8 0. 5G decyl B-dPcyl- 3. 3 0. 57 3. 4 l. 36 3. 4 0.87 tridecyl B-tridec 3.0 0. 75 3. 0 0. 81 3. 0 0. 73 decyl B-non 3. 4 1. 8. 4 0. 74 3. 4 0. 66 2-ethylhexy] B-trldccyl. 3. 3 0. 62 3. 5 0. 34 3. 4 0. 22 2-ethylhexyl decyl 1 3. 4 0.22 3. 6 0. 71

1 Determined at 18 0.

Electrical apparatus comprising conducting elements which in operation have a difference in electrical potential and which have a dielectric comprising the present propionates interposed between said elements function admirably not only because of the high volume rcsistivity, good dielectric constant and low power factor values of said propionates, but also because the normally liquid, branched chain higher alkyl B-alkoxypropion-ates have very low pour points. Operation of the apparatus at very low temperature without danger of freezing is thereby permitted. Pour points of the branched chain alkyl ,S-alkoxypropionates of the above tables are shown below:

-Oxypropionate: Pour point, F. Isooctyl fi-isooctyl minus 20 Nonyl B-nonyl .a minus 80 Decyl fi-decyl minus 65 Tridecyl fl-tridecyl minus 70 Decyl fi-nonyl minus 65 2-ethylhexyl ,H-tridecyl minus 65 Thus paper capacitors prepared, e. g., by impregnating kraft tissue paper with the branched chain nonyl ,G-nonyb oxypropionate, inter-leaving the impregnated tissues be tween aluminum foil, and rolling the interleaved assembly were useful at temperatures of down to about minus 80' R, which is the pour point of said nonyl compound.

Electrical apparatus comprising the present branched chain higher alkyl dalkoxypropionates is versatile in utility also because of the very good high temperature properties of said propionatcs, which are generally high boiling liquids having flash points of over 300 F. For example, transformers containing the branched chain tridecyl p-tridecyloxypropionate function at temperatures of as low as minus F., which is the pour point of said tridecyl compound and up to a temperature of 430 R, which is the flash point of the tridecyl compound.

As hcreinhefore disclosed the present branched chain higher alkyl fi-alkoxypropionates may be employed per se as the dielectric liquid media of electrical apparatus, or they may be combined with up to substantially equal parts by weight of one or more other dielectric liquids, such as certain liquid petroleum hydrocarbons, the partially chlorinated biphenyls, trichlorobenzene, benzene, chlorinated naphthalene, chlorinated diphenyl ketone, chlorinated diphenyl oxide, chlorinated diphenylmethane, chlorinated diphenylethane, chlorinated benzene, chlorinated toluene, chlorinated nitrobiphenyl, chlorinated alkylated benzenes, chlorinated alkylated 'biphenyls, ethyl trichlorobenzene, ethyl tctrachlorobenzene, ethyl pentachlorobenzene, chlorinated terphenyls, chlorinated quaterphenyls, chlorinated parafiinic hydrocarbons, chlorinated alicyclic hydrocarbons, chlorinated oxygen-containing organic compounds, chlorinated rubber, chlorinated polymers, chlorinated fats, chlorinated vegetable oils, chlorinated animal oils, chlorinated mineral oils or mixtures of one or more of these.

What I claim is:

1. Electrical apparatus comprising, in combination, metallic conducting elements disposed in spaced relation ship to each other and adapted during operation of the apparatus to have a ditference in electrical potential therebetween and, interposed between said elements for insulating one from the other, a liquid dielectric medium comprising an alkyl fl-alkoxypropionate of the formula wherein R and R are branched chain alkyl radicals of from 8 to 18 carbon atoms.

2. The electrical apparatus defined in claim 1, further limited in that the alkyl ,Q-alkoxypropionate is a Z-ethylhexyl B-tridecyloxypropionate wherein the tridecyl radical is branched and is derived from OX0 process tridecanol.

3. The electrical apparatus defined in claim 1, further limited in that the alkyl fl-alkoxypropionatc is nonyl fl-nonyloxypropionate wherein the nonyl radicals are branched and are derived from 0x0 process nonanol.

4. The electrical apparatus defined in claim 1, further limited in that the alkyl B-alkoxypropionate is tridecyl fl-tridecyloxyprcpionate wherein the tridecyl radicals are branched and are derived from Ono process tridccanol.

5. The electrical apparatus defined in claim l, further limited in that the alkyl ,B-alkoxypropionate is decyl finonyloxypropionate wherein the decyl and nonyl radicals are branched and are derived from OX0 process decanol and nonanol, respectively.

6. The electrical apparatus defined in claim 1. further limited in that the alkyl B-alkoxypropionate is decyl B- decyloxypropionate wherein the decyl radical is branched and is derived from OX0 process decanol.

References Cited in the tile of this patent UNITED STATES PATENTS Frost et a1. Aug. 6. 1957 OTHER REFERENCES 

1. ELECTRICAL APPARATUS COMPRISING, IN COMBINATION, METALLIC CONDUCTING ELEMENTS DISPOSED IN SPACED RELATIONSHIP TO EACH OTHER AND ADAPTED DURING OPERATION OF THE APPARATUS TO HAVE A DIFFERENCE IN ELECTRICAL POTENTIAL THEREBETWEEN AND, INTERPOSED BETWEEN SAID ELEMENTS FOR INSULATING ONE FROM THE OTHER, A LIQUID DIELECTRIC MEDIUM COMPRISING AN ALKYL B-ALKOXYPROPIONATE OF THE FORMULA 